Donald H. Meclelland disclosed a Maintenance-free type Lead Acid Cell in his U.S. Pat. No. 3,862,861 which is characterized by structurally free, non-self-supporting plates separated from one another with highly absorbent flexible separators containing electrolyte and constrained within a container such that mechanical integrity is imparted to obtain a unitary self-supporting structure. However such a lead acid cell has the following defects:
1. Even such a cell provides a valve means 23, a yieldable cap of the central vent of the cell, to release any excessively high pressure in the cell and if such a cell is inferentially expected to be a rechargeable storage battery as subject to a overcharged condition, the electric terminals are still connected without being cut off, thereby resulting in much loss of entrained electrolyte droplets as laden in the venting gas and possibly causing unsafe situation.
2. One of its preferred embodiments disclosed a spiral configuration by spirally winding the positive and negative plates, and the separator material disposed between the two plates, which however may be squeezed to deform the electrodes or to break the separator to cause short-circuit drawback between the electrodes to thereby reduce the output electricity of the plates and decrease the overall efficiency of the cell.
The present inventor has found the defects of the prior Donald's cell and invented the present rechargeable storage battery and its making method.